Rotary internal combustion engine with pilot subchamber

ABSTRACT

A Wankel engine having an insert in the peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening, a pilot fuel injector having a tip received in the subchamber, an ignition element having a tip received in the subchamber, and a main fuel injector extending through the housing and having a tip communicating with the cavity at a location spaced apart from the insert.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority on provisional U.S. application No. 61/512,593 filed Jul. 28, 2011, the entire contents of which are incorporated by reference herein.

TECHNICAL FIELD

The application relates generally to a compound engine system including a rotary internal combustion engine, more particularly, to such a system employing heavy fuels.

BACKGROUND OF THE ART

Rotary engines, such as for example Wankel engines, use the eccentric rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor includes a number of apex or seal portions which remain in contact with a peripheral wall of the rotor cavity of the engine throughout the rotational motion of the rotor to create a plurality of rotating chambers when the rotor rotates.

Wankel engines are typically used with gasoline or similar fuel, with a single fuel injector or with two spaced apart fuel injectors. The fuel injector(s) may be located in a recess adjacent the combustion chamber and defined integrally through the engine housing, to communicate with an ignition member such as for example a spark plug. However, known arrangements are not optimized for use in a compound cycle engine system and/or for use with so-called heavy fuels, such as kerosene, and thus room for improvement exists.

SUMMARY

In one aspect, there is provided a rotary engine comprising a stator body having an internal cavity defined by two axially spaced apart end walls and a peripheral wall extending between the end walls, the cavity having an epitrochoid shape defining two lobes, a rotor body having three circumferentially spaced apex portions, the rotor body being engaged to an eccentric portion of a shaft to rotate and perform orbital revolutions within the cavity with each of the apex portions remaining in sealing engagement with the peripheral wall and separating three rotating chambers of variable volume defined in the cavity around the rotor body, an insert in the peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, the insert having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening, a pilot fuel injector having a tip received in the subchamber, an ignition element having a tip received in the subchamber, and a main fuel injector extending through the stator body and having a tip communicating with the cavity at a location spaced apart from the insert.

In another aspect, there is provided a stator body for a Wankel engine comprising two axially spaced apart end walls, a peripheral wall extending between the end walls and defining an internal cavity therewith, the cavity having an epitrochoid shape defining two lobes, an insert in the peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, the insert having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening, at least one of the insert and the peripheral wall having a pilot fuel injector elongated hole defined therethrough communicating with the subchamber and sized to receive a pilot fuel injector therein, at least one of the insert and the peripheral wall having an ignition element elongated hole defined therethrough communicating with the subchamber and sized to receive an ignition element therein, and the peripheral wall having a main fuel injector elongated hole defined therethrough spaced apart from the insert and sized to receive a main fuel injector therein.

In yet another aspect, there is provided a method of injecting heavy fuel into a Wankel engine having rotating chambers each having a volume varying between a minimum volume and a maximum volume, the method comprising injecting a minor portion of the heavy fuel into a subchamber defined adjacent to and in sequential communication with each of the rotating chambers and having a subchamber volume corresponding to from 5% to 25% of a sum of the minimum volume and the subchamber volume, igniting the heavy fuel within the subchamber, partially restricting a flow of the ignited heavy fuel from the subchamber to the rotating chambers, and injecting a remainder of the heavy fuel into each of the rotating chambers sequentially, independently of and spaced apart from the subchamber.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a partial, schematic cross-sectional view of a rotary internal combustion engine in accordance with a particular embodiment;

FIG. 2 is a schematic cross-sectional view of an insert of the engine of FIG. 1;

FIG. 3 is a schematic cross-sectional view of an insert in accordance with another embodiment; and

FIG. 4 is a schematic cross-sectional view of an insert in accordance with a further embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a rotary internal combustion engine 10 known as a Wankel engine is schematically and partially shown. In a particular embodiment, the rotary engine 10 is used in a compound cycle engine system such as described in Lents et al.'s U.S. Pat. No. 7,753,036 issued Jul. 13, 2010 or as described in Julien et al.'s U.S. Pat. No. 7,775,044 issued Aug. 17, 2010, the entire contents of both of which are incorporated by reference herein. The compound cycle engine system may be used as a prime mover engine, such as on an aircraft or other vehicle, or in any other suitable application. In any event, in such a system, air is compressed by a compressor before entering the Wankel engine, and the engine drives one or more turbine(s) of the compound engine. In another embodiment, the rotary engine 10 is used without a turbocharger, with air at atmospheric pressure.

The engine 10 comprises an outer body 12 having axially-spaced end walls 14 with a peripheral wall 18 extending therebetween to form a rotor cavity 20. The inner surface 19 of the peripheral wall 18 of the cavity 20 has a profile defining two lobes, which is preferably an epitrochoid.

An inner body or rotor 24 is received within the cavity 20, with the geometrical axis of the rotor 24 being offset from and parallel to the axis of the outer body 12. The rotor 24 has axially spaced end faces 26 adjacent to the outer body end walls 14, and a peripheral face 28 extending therebetween. The peripheral face 28 defines three circumferentially-spaced apex portions 30 (only one of which is shown), and a generally triangular profile with outwardly arched sides. The apex portions 30 are in sealing engagement with the inner surface of peripheral wall 18 to form three rotating working chambers 32 (only two of which are partially shown) between the inner rotor 24 and outer body 12. A recess 38 is defined in the peripheral face 28 of the rotor 24 between each pair of adjacent apex portions 30, to form part of the corresponding chamber 32.

The working chambers 32 are sealed. Each rotor apex portion 30 has an apex seal 52 extending from one end face 26 to the other and protruding radially from the peripheral face 28. Each apex seal 52 is biased radially outwardly against the peripheral wall 18 through a respective spring. An end seal 54 engages each end of each apex seal 52, and is biased against the respective end wall 14 through a suitable spring. Each end face 26 of the rotor 24 has at least one arc-shaped face seal 60 running from each apex portion 30 to each adjacent apex portion 30, adjacent to but inwardly of the rotor periphery throughout its length. A spring urges each face seal 60 axially outwardly so that the face seal 60 projects axially away from the adjacent rotor end face 26 into sealing engagement with the adjacent end wall 14 of the cavity. Each face seal 60 is in sealing engagement with the end seal 54 adjacent each end thereof.

Although not shown in the Figures, the rotor 24 is journaled on an eccentric portion of a shaft and includes a phasing gear co-axial with the rotor axis, which is meshed with a fixed stator phasing gear secured to the outer body co-axially with the shaft. The shaft rotates the rotor 24 and the meshed gears guide the rotor 24 to perform orbital revolutions within the rotor cavity. The shaft rotates three times for each complete rotation of the rotor 24 as it moves around the rotor cavity 20. Oil seals are provided around the phasing gear to prevent leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face 26 and outer body end wall 14.

At least one inlet port (not shown) is defined through one of the end walls 14 or the peripheral wall 18 for admitting air (atmospheric or compressed) into one of the working chambers 32, and at least one exhaust port (not shown) is defined through one of the end walls 14 or the peripheral wall 18 for discharge of the exhaust gases from the working chambers 32. The inlet and exhaust ports are positioned relative to each other and relative to the ignition member and fuel injectors (further described below) such that during each rotation of the rotor 24, each chamber 32 moves around the cavity 20 with a variable volume to undergo the four phases of intake, compression, expansion and exhaust, these phases being similar to the strokes in a reciprocating-type internal combustion engine having a four-stroke cycle.

In a particular embodiment, these ports are arranged such that the rotary engine 10 operates under the principle of the Miller or Atkinson cycle, with its volumetric compression ratio lower than its volumetric expansion ratio. In another embodiment, the ports are arranged such that the volumetric compression and expansion ratios are equal or similar to one another.

An insert 34 is received in a corresponding hole 36 defined through the peripheral wall 18 of the outer body 12, for pilot fuel injection and ignition. The peripheral wall 18 also has a main injector elongated hole 40 defined therethrough, in communication with the rotor cavity 20 and spaced apart from the insert 34. A main fuel injector 42 is received and retained within this corresponding hole 40, with the tip 44 of the main injector 42 communicating with the cavity 20 at a point spaced apart from the insert 34. The main injector 42 is located rearwardly of the insert 34 with respect to the direction R of the rotor rotation and revolution, and is angled to direct fuel forwardly into each of the rotating chambers 32 sequentially with a tip hole pattern designed for an adequate spray.

Referring particularly to FIG. 2, the insert includes an elongated body 46 extending across a thickness of the peripheral wall 18, with an enlarged flange 48 at its outer end which is biased away from a shoulder 50 defined in the peripheral wall 18, and against a gasket (not shown) made of an appropriate type of heat resistant material such as a silica based material. A washer 56, such as for example a steel or titanium washer, and spring 58, such as for example a wave spring or a Belleville spring, are provided between the flange 48 and the shoulder 50 of the peripheral wall 18. The spring 58 biases the body 46 against a cover 62 having a cross-section greater than that of the hole 36 and extending over an outer surface 64 of the peripheral wall 18. The cover 62 is connected to the peripheral wall 18, for example through brazing. Alternate types of connections can also be used, including but not limited to a connection through fasteners such as bolts, to help facilitate replacement of the insert if necessary.

The insert body 46 has an inner surface 66 which is continuous with the inner surface 19 of the peripheral wall 20 to define the cavity 20. The insert hole 36 in the wall 18 defines a flange 68 extending in the insert hole 36 adjacent the inner surface 19, and the inner end of the insert body 46 is complementarily shaped to engage this flange 68, with a gasket 70 being received therebetween.

The insert body 46 is made of a material having a greater heat resistance than that of the peripheral wall 18, which in a particular embodiment is made of aluminium. In this particular embodiment, the insert body 46 is made of an appropriate type of ceramic.

The insert body 46 has a pilot subchamber 72 defined therein in communication with the rotor cavity 20. In the embodiment shown, the subchamber 72 has a circular cross-section; alternate shapes are also possible. The subchamber 72 communicates with the cavity through at least one opening 74 defined in the inner surface 66. The subchamber 72 has a shape forming a reduced cross-section adjacent the opening 74, such that the opening 74 defines a restriction to the flow between the subchamber 72 and the cavity 20. The opening 74 may have various shapes and/or be defined by a pattern of multiple holes.

The peripheral wall 18 has a pilot injector elongated hole 76 defined therethrough in proximity of the insert 34, extending at a non-zero angle with respect to a surface of an outer wall of the insert 34, and in communication with the subchamber 72. A pilot fuel injector 78 is received and retained within the corresponding hole 76, with the tip 80 of the pilot injector 78 being received in the subchamber 72. As can be seen in FIG. 2, the insert body 46 has an injector opening defined therethrough providing the communication between the pilot injector elongated hole 76 and the subchamber 72, and the tip 80 of the pilot injector 78 is received in the subchamber 72 through this injector opening, with a major part of the pilot injector 78 being received in the pilot injector elongated hole 76 outside of the insert 34.

The insert body 46 and cover 62 have an ignition element elongated hole 82 defined therein extending along the direction of the transverse axis T of the outer body 12, also in communication with the subchamber 72. An ignition element 84 is received and retained within the corresponding hole 82, with the tip 86 of the ignition element 84 being received in the subchamber 72. In the embodiment shown, the ignition element 84 is a glow plug. Alternate types of ignition elements 84 which may be used include, but are not limited to, plasma ignition, laser ignition, spark plug, microwave, etc.

The pilot injector 78 and main injector 42 inject heavy fuel, e.g. diesel, kerosene (jet fuel), equivalent biofuel, etc. into the chambers 32. In a particular embodiment, at least 0.5% and up to 20% of the fuel is injected through the pilot injector 78, and the remainder is injected through the main injector 42. In another particular embodiment, at most 10% of the fuel is injected through the pilot injector 78. In another particular embodiment, at most 5% of the fuel is injected through the pilot injector 78. The main injector 42 injects the fuel such that each rotating chamber 32 when in the combustion phase contains a lean mixture of air and fuel.

Referring to FIG. 3, an insert 134 according to another embodiment is shown, engaged to the same outer body 12. The insert 134 extends across a thickness of the peripheral wall 18, and includes an inner body portion 146 and an outer body portion 162 which are attached together, for example through a high temperature braze joint 188. The outer body portion 162 has an enlarged flange 148 at its outer end which abuts the outer surface 64 of the peripheral wall 18 and is connected thereto, for example through bolts with appropriate sealing such as a gasket or crush seal (not shown). Alternate types of connections can also be used, including but not limited to a brazed connection.

The inner body portion 146 has an inner surface 166 which is continuous with the inner surface 19 of the peripheral wall 18 to define the cavity 20. The inner end of the inner body portion 146 is complementarily shaped to engage the flange 68 extending in the insert hole 36 adjacent the inner surface 19, with a gasket 70 being received therebetween.

In this particular embodiment, the body portions 146, 162 are made of an appropriate type of super alloy such as a Nickel based super alloy.

The pilot subchamber 72 is defined in the insert 134 at the junction between the body portions 146, 162, with the inner body portion 146 defining the opening 74 for communication between the subchamber 72 and the cavity 20. The outer body portion 162 has the ignition element elongated hole 82 defined therein along the direction of the transverse axis T and in communication with the subchamber 72. The ignition element 84 is received and retained within the corresponding hole 82, for example through threaded engagement. As in the previous embodiment, the tip 86 of the ignition element 84 is received in the subchamber 72.

Referring to FIG. 4, an insert 234 according to another embodiment is shown. The insert 234 is received in a corresponding hole 236 defined through the peripheral wall 18. The insert 234 includes an inner body portion 246 and an outer body portion 262 which are attached together, for example through a high temperature braze joint, with the subchamber 72 being defined at the junction of the two portions 246, 262. The inner body portion 246 defines the opening 74 for communication between the subchamber 72 and the cavity 20.

The outer body portion 262 has the ignition element elongated hole 82 defined therethrough in communication with the subchamber 72. The outer body portion 262 includes an inner enlarged section 245 connected to the inner body portion 246 and defining the subchamber 72. The enlarged section 245 extends substantially across the width of the hole 236 around the subchamber 72, then tapers to a reduced width section 247 extending therefrom. The reduced width section 247 has at its outer end an enlarged flange 248 which abuts a shoulder 250 defined in the outer surface 64 of the peripheral wall 18 around the hole 236. An outer section 249, which in the embodiment shown has a width intermediate that of the sections 245 and 247, extends outwardly from the flange 248. The flange is connected to the shoulder, for example through bolts (not shown) with appropriate sealing such as a crush seal or a gasket (not shown) made of high temperature material, for example a silica based material or grafoil, between the flange 248 and shoulder 250. Alternate types of connections can also be used.

The inner body portion 246 has an inner surface 266 which is continuous with the inner surface 19 of the peripheral wall 18 to define the cavity 20. The inner body portion 246 includes a groove defined therearound near the inner surface 266, in which an appropriate seal 251, for example a silica based gasket tape, is received in contact with the walls of the insert hole 236. In this embodiment, the walls of the insert holes 236 are straight adjacent the inner surface 19, i.e. there is no flange adjacent the inner surface 19.

The volume of the subchamber 72 in the insert 34, 134, 234 is selected to obtain a stoichiometric mixture around ignition within an acceptable delay, with some of the exhaust product from the previous combustion cycle remaining in the subchamber 72. In a particular embodiment, the volume of the subchamber 72 is at least 0.5% and up to 3.5% of the displacement volume, with the displacement volume being defined as the difference between the maximum and minimum volumes of one chamber 32. In another particular embodiment, the volume of the subchamber 72 corresponds to from about 0.625% to about 1.25% of the displacement volume.

The volume of the subchamber 72 may also be defined as a portion of the combustion volume, which is the sum of the minimum chamber volume V_(min) (including the recess 38) and the volume of the subchamber V₂ itself. In a particular embodiment the subchamber 72 has a volume corresponding to from 5% to 25% of the combustion volume, i.e. V₂=5% to 25% of (V₂+V_(min)). In another particular embodiment, the subchamber 72 has a volume corresponding to from 10% to 12% of the combustion volume, i.e. V₂=10% to 12% of (V₂+V_(min)).

The subchamber 72 may help create a stable and powerful ignition zone to ignite the overall lean main combustion chamber 32 to create the stratified charge combustion. The subchamber 72 may improve combustion stability, particularly but not exclusively for a rotary engine which operates with heavy fuel below the self ignition of fuel. The insert 34, 134, 234 made of a heat resistant material may advantageously create a hot wall around the subchamber which may further help with ignition stability.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention(s) disclosed. For example, the mechanical arrangement of the Wankel engine described above is merely one example of many possible configurations which are suitable for use with the present invention(s). Any suitable injector configuration and arrangement may be used. Hence, modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. 

The invention claimed is:
 1. A rotary engine comprising: a stator body having an internal cavity defined by two axially spaced apart end walls and a peripheral wall extending between the end walls, the cavity having an epitrochoid shape defining two lobes; a rotor body having three circumferentially spaced apex portions, the rotor body being engaged to an eccentric portion of a shaft to rotate and perform orbital revolutions within the cavity with each of the apex portions remaining in sealing engagement with the peripheral wall and separating three rotating chambers of variable volume defined in the cavity around the rotor body, the volume of each chamber varying between a minimum volume and a maximum volume, a difference between the maximum volume and the minimum volume defining a displacement volume; an insert in the peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, the insert having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening, the subchamber having a volume of at least about 0.5% of the displacement volume and at most about 3.5% of the displacement volume; a pilot fuel injector having a tip received in the subchamber, the tip of the pilot fuel injector extending through an injector opening defined through the insert; an ignition element received within an ignition element hole defined through the insert, the ignition element having a tip received in the subchamber; and a main fuel injector extending through the stator body and having a tip communicating with the cavity at a location spaced apart from the insert.
 2. The engine as defined in claim 1, wherein the subchamber has a volume of at least 0.625% of the displacement volume.
 3. The engine as defined in claim 1, wherein the subchamber has a volume of about 1.25% the displacement volume.
 4. The engine as defined in claim 1, wherein the subchamber has a volume corresponding to from 5% to 25% of a sum of the minimum volume and the volume of the subchamber.
 5. The engine as defined in claim 3, wherein the volume of the subchamber corresponds to from 10% to 12% of the sum of the minimum volume and the volume of the subchamber.
 6. The engine as defined in claim 1, wherein the insert is made of ceramic or super alloy.
 7. The engine as defined in claim 1, wherein the pilot injector extends through the peripheral wall at a non-zero angle with respect to a surface of an outer wall of the insert with only a portion thereof extending within the insert.
 8. The engine as defined in claim 1, further comprising a heavy fuel source in communication with the fuel injectors.
 9. A stator body for a Wankel engine comprising: two axially spaced apart end walls; a peripheral wall extending between the end walls and defining an internal cavity therewith, the cavity having an epitrochoid shape defining two lobes; an insert in the peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, the insert having a subchamber defined therein and having an inner surface bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening; the insert having an injector opening defined therethrough communicating with the subchamber, the injector opening being sized to receive a tip of a pilot fuel injector therethrough; the insert having an ignition element elongated hole defined therethrough communicating with the subchamber and sized to receive an ignition element therein; the peripheral wall having a pilot fuel injector elongated hole defined therethrough at a non-zero angle with respect to a surface of an outer wall of the insert and communicating with the subchamber through the injector opening of the insert, the pilot fuel injection elongated hole being sized to directly receive the pilot fuel injector therein; and the peripheral wall having a main fuel injector elongated hole defined therethrough spaced apart from the insert and sized to receive a main fuel injector therein.
 10. The stator body as defined in claim 9, wherein the insert is made of ceramic or super alloy.
 11. The stator body as defined in claim 9, wherein the pilot fuel injection elongated hole is sized to receive a major part of the pilot fuel injector.
 12. A method of injecting heavy fuel into a Wankel engine having rotating chambers each having a volume varying between a minimum volume and a maximum volume with a difference between the maximum volume and the minimum volume defining a displacement volume, the method comprising: injecting a minor portion of the heavy fuel into a subchamber defined adjacent to and in sequential communication with each of the rotating chambers and having a subchamber volume of at least about 0.5% of the displacement volume and at most about 3.5% of the displacement volume; igniting the heavy fuel within the subchamber; creating a hot wall around the subchamber by providing the subchamber in an insert received in a wall of a stator of the engine, the insert being made of a material more resistant to high temperature than that of the wall; partially restricting a flow of the ignited heavy fuel from the subchamber to the rotating chambers; and injecting a remainder of the heavy fuel into each of the rotating chambers sequentially, independently of and spaced apart from the subchamber.
 13. The method as defined in claim 12, wherein injecting a minor portion of the heavy fuel into the subchamber includes injecting from 0.5% to 20% of the heavy fuel.
 14. The method as defined in claim 12, wherein injecting a minor portion of the heavy fuel into the subchamber includes injecting from 5% to 10% of the heavy fuel.
 15. The method as defined in claim 12, wherein injecting the minor portion of the heavy fuel is done into the subchamber with the subchamber volume corresponding to from 10% to 12% of the sum of the minimum volume and the subchamber volume.
 16. The method as defined in claim 12, wherein the insert is received in a peripheral wall of the engine.
 17. The method as defined in claim 12, wherein injecting the minor portion of the heavy fuel is done in an angled direction with respect to a central transverse axis of a stator of the engine. 